Method of fabricating canister with porous plastic ends

ABSTRACT

A canister including an elongated hollow plastic body having a wall with inner and outer surfaces, an edge portion on the wall defining an open end, an end on the edge portion extending transversely to the inner and outer surfaces, a porous plastic member having an outer edge portion extending across the open end and fused to the end, an inner portion on the porous plastic member located radially inwardly of the outer edge portion and extending into the body and fused to the inner surface of the wall adjacent the end thereof, and a gas-treating material in the body. A method of fabricating the above canister including the steps of applying pressure and vibratory welding energy to the porous member to thereby cause the member which was originally planar in shape to have its outer edge compressed against the end of the body and fused thereto and the central portion inwardly of the outer edge forced into the body and its outer edge fused to the inner surface of the body adjacent the end.

This is a continuation of application Ser. No. 08/449,352 filed May 24,1995, now U.S. Pat. No. 5,833,784, which is a division of priorapplication Ser. No. 08/219,400, filed Mar. 29, 1994, now U.S. Pat. No.5,503,662, dated Apr. 2, 1996.

BACKGROUND OF THE INVENTION

The present invention relates to an improved canister for containinggas-treating material such as a desiccant or oxygen absorber.

By way of background, there are in use canisters of various types foradsorbing moisture from pharmaceutical containers and for treatingenvironments by absorbing gases therefrom. One type of prior canister isdisclosed in U.S. Pat. No. 4,772,300 wherein a web-bonded polyethyleneis secured to the ends of a polyethylene body by means of ultrasonicwelding. However, there was no consistency in obtaining good uniformwelds therebetween. It is believed that the deficiency was due to thefact that the interface of both parts did not melt at the same time tocreate a good fused bond.

SUMMARY OF THE INVENTION

It is the primary object of the present invention to provide a canisterwherein at least one porous end thereof is firmly secured to the body bymeans of vibratory welding, thereby producing a secure bondtherebetween.

Another object of the present invention is to provide an improvedcanister wherein a porous end is secured to the body at two annularjoints thereby assuring bonding therebetween which virtually precludesseparation which could lead to spilling of the contents of the canister.

A further object of the present invention is to provide an improvedmethod for fabricating a canister having a porous end. Other objects andattendant advantages of the present invention will readily be perceivedhereafter.

The present invention relates to a canister comprising an elongatedhollow plastic body having a wall, inner and outer surfaces on saidwall, an edge portion on said wall defining an open end, an end on saidedge portion extending transversely to said inner and outer surfaces,and a porous plastic member having an outer edge portion extendingacross said open end and being sufficiently stiff so as to be fused tosaid end by vibratory welding.

The present invention also relates to a canister comprising an elongatedhollow plastic body having a wall, inner and outer surfaces on saidwall, an edge portion on said wall defining an open end, an end on saidedge portion extending transversely to said inner and outer surfaces,and a porous plastic member having an outer edge portion extendingacross said open end and fused to said end and having an inner portionlocated radially inwardly of said outer edge and extending into saidbody and fused to said inner surface of said wall adjacent said end. Thecanister can contain a gas-treating material which adsorbs moisture orabsorbs other gases such as oxygen.

The present invention also relates to a method of fabricating a canistercomprising the steps of providing an elongated tubular plastic bodyhaving an inner surface and an outer surface and an edge portion on saidbody defining an opening and an end on said edge portion, providing aporous sheet-like plastic member which is sufficiently stiff so that itwill not buckle when subjected to pressure in a direction transversethereto and to vibratory welding energy substantially parallel theretoboth of which are experienced when it is subjected to vibratory welding,positioning said porous sheet-like plastic member across said openingand in engagement with said end, and applying pressure in a directiontransverse to said sheet-like member and vibratory welding energy in adirection substantially parallel to said sheet-like member to bond saidsheet-like member to said end.

The present invention also relates to a method of fabricating a canistercomprising the steps of providing an elongated tubular plastic bodyhaving an inner surface and an outer surface and an edge portion on saidbody defining an opening and an end on said edge portion, positioning aporous sheet-like plastic member across said opening in engagement withsaid end, applying pressure to said member to force an outer edgeportion thereof against said end and to force an inner portion locatedinwardly of said outer edge portion into said opening, and applyingvibratory welding energy to said member to effect fusion between saidouter edge portion of said member and said end and to also effect fusionbetween said inner portion of said member and said inner surface of saidedge portion adjacent said end.

The various aspects of the present invention will be more fullyunderstood when the following portions of the specification are read inconjunction with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is side elevational view of the improved canister of the presentinvention;

FIG. 2 is a plan view taken substantially in the direction of arrows2--2 of FIG. 1;

FIG. 3 is a cross sectional view taken substantially along line 3--3 ofFIG. 1;

FIG. 4 is an enlarged fragmentary cross sectional view takensubstantially along line 3--3 of FIG. 1 and showing the details at thelocations between the body and the porous ends of the canister;

FIG. 5 is a schematic fragmentary plan view showing a tube being cutinto lengths for providing the bodies of the canisters;

FIG. 6 is a schematic fragmentary side elevational view in cross sectiondepicting the next step in fabricating the canisters by attaching porousends to the first ends of the canisters by vibratory welding after theyhave been placed in a fixture;

FIG. 7 is a view similar to FIG. 6 but showing the next step in theprocess, namely, trimming excess porous materials away from the ends ofthe canisters;

FIG. 8 is a schematic view in cross section showing the next step,namely, filling the open ends of the canisters with gas-treatingmaterial;

FIG. 9 is a view similar to FIG. 6 and showing the next step, namely,bonding porous members to the opposite ends of the canister bodies afterthey have been filled with gas-treating material; and

FIG. 10 is a view similar to FIG. 7 and showing the excess porousmaterial being trimmed from the ends of the canisters.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The improved gas-treating canister 10 of the present invention includesa cylindrical canister body 11 fabricated of high density polyethyleneand having an outer surface 12 and an inner surface 13. Porous closuremembers of high density polyethylene 14 are bonded to end portions 15 ofcanister body 11 by vibratory welding. More specifically, porous closuremembers 14 include outer edge portions 19 which are bonded to ends 17 atthe junctions therebetween. In addition, porous members 14 includecentral inner portions 20 which are located within body 11 and havesurface portions 21 located radially inwardly of outer edge portions 19.The outer edges 21 of portions 20 are bonded to the inner surface at 22adjacent to ends 17. In addition, annular beads 26 are formed during thevibratory welding process and provide an additional bond between porousmembers 14 and body 11. Thus, each member 14 is bonded at threelocations, namely, at annular end 17 and at annular surface 22 adjacentend 17 and at annular beads 26, to thereby securely contain the granularmaterial 23 within the canister 10.

The canister 10 possessing the above-described multiple bond on members14 is fabricated in the manner shown in FIGS. 5-10. The first step inthe process is to provide bodies 11. These can be obtained by cutting anextruded high density polyethylene tube 24 into bodies 11 by means of asuitable cutting blade 25 associated with a tube rotating and advancingdevice 25', or the bodies 11 can be obtained in any other suitablemanner. The next step is to press fit bodies 11 into a fixture 27 withonly very small end portions 29 at both ends of bodies 11 protrudingbeyond the surfaces 30 of fixture 27. This causes them to be heldsecurely during the subsequent vibratory welding operations. Thereafter,a sheet of porous high density polyethylene 31 is laid across the openends of canister bodies 11. Sheet 31 has a matte surface and a shinysurface. Preferably the matte surface of sheet 31 is placed incontiguous relationship to the ends of bodies 11, but the shiny surfacecan be placed against the ends of the bodies 11. Thereafter, a vibratorywelding die 32 is applied to sheet 31 with sufficient pressure tocompress the portions 19 (FIG. 4) which are bonded to the ends 17 and toalso force the uncompressed central portions 20 into the interior of thebody 11. The protruding end portions 29, which are opposite to the endsto which the vibratory die 32 is applied, are supported by base portion28 associated with fixture 27. The pressure which is applied is depictedby arrows 33 and the vibratory motion, which is horizontal, is depictedby arrows 34. Porous plastic sheet 31 is sufficiently stiff so that itwill not buckle when subjected to the pressure and the vibratory motion.It is this combination of pressure and horizontal vibratory motion whicheffects the multiple bonds discussed above relative to FIGS. 3 and 4. Itis believed that the bead 26 is formed as a result of flow of moltenpolyethylene which is produced during the vibratory welding process.

After the porous plastic sheet 31 has been bonded to the plurality ofbodies 11, a trimming die 35 is applied to the sheet 31, as depicted inFIG. 7, and the excess material of sheet 31 is trimmed away so that onlythe smooth outer edge of member 14 exists at 37 on each of the bodies11. As shown in FIG. 7, trimming die 35 consists of a plurality ofcircular knives 38 which trim away the material of sheet 31 which liesoutside of ends 14.

The next step of the process is to place the bodies which were formed inFIG. 7 into an inverted position by inverting fixture 27 and fill thebodies 11 with granular material 23 from a source such as hoppers 41.Thereafter, another sheet of porous high density plastic material 31 isplaced across the open ends of bodies 11 which are held in fixture 27,and a vibratory welding die 32 applies pressure depicted by arrows 33and horizontal vibration depicted by arrow 34 to the top of plasticsheet 31 to thereby form ends 14 as described above relative to FIGS. 4and 7. During this procedure, the ends of bodies 11 which werepreviously closed with porous ends 14 are supported on base 28.Thereafter, a trimming die 35 is utilized to trim the excess porousmaterial 31 away from the ends of bodies 11.

In specific canisters which have been fabricated, the bodies 11 are highdensity polyethylene. The bodies 11 have an outer diameter ofapproximately 0.55 inches, a length of approximately 0.630 inches and awall thickness of approximately 0.035 inches and they have beenfabricated from a product known as Phillips HM520BN FDA grade highdensity polyethylene. When the bodies 11 are properly positioned inbores 26 of fixture 27, they protrude about 0.030 inches at each end.

In the specific canisters which have been fabricated, the sheets 31 areporous high density polyethylene which is known under the trademarkPOREX which is a proprietary product of Porex Technologies of Fairburn,Ga. The sheet 31 of POREX is originally 0.035 inches plus or minus 0.005inches thick. It has an air flow of 1900-3800 milliliters per minutethrough a one-inch diameter disc at a pressure of 1.2 inches of water.It will be appreciated that other porosities may be used, depending onthe specific requirements of any particular application. The sheet 31has a stiffness which is measured as the apparent bending modulus whichis indicated on a straight line graph of Deflection versus ApparentBending which is a plot of degrees deflection versus psi wherein thedegrees are between 8 and 30 and the psi is between 327 and 1226 whentested on a one inch-pound Tinius Olsen Stiffness Testing Machine(Condensation of ASTM D 747) wherein the span length is 0.5 inches andthe sheet width is 0.5 inches and the sheet thickness is 0.04 inches andthe load is 0.15 pounds with a load scale reading of 50%. It will beappreciated that other stiffnesses are acceptable. The criterion is thatthe sheet 31 should be sufficiently stiff so that it will not bucklewhen subjected to the forces encountered during vibratory welding.

Each porous member 14 retains the 0.035 inch dimension in the centralportion 20 which enters body 11. The outer edge portion 19, however, iscompressed to about 0.010 inches as a result of the above-describedvibration welding under pressure. It will be appreciated that othertypes of porous polyethylene which have other parameters can be used.

The vibration welding process described above utilizes a clamping forceor pressure of between about 700-900 pounds per square inch, and itincludes a cycle time of 2 seconds which includes a weld time of 1.5seconds with a subsequent hold time of 0.5 seconds being held at themaximum clamping force which is applied. The vibratory welding producesa sinusoidal waveform having an amplitude of 0.070 inches and a nominalfrequency of 240 Hz. The stiffness of the material 31 permits the use ofvibratory welding. In this respect, the material would tend to oscillateif it were not sufficiently stiff, and therefore it would tend tobuckle. However, because the material 31 is sufficiently stiff, it willnot buckle. The vibratory welding die which was used in the specificinstance is known under the name of BRANSON, and is manufactured byBranson Plastic Joining, Inc. of Henrietta, N.Y. The foregoing vibratorywelding process causes fusion between members 14 and body 11 at ends 17and at surfaces 22 and at beads 26. This fusion is obtained because bothparts 11 and 14 in both interface areas 17 and 22 melt at substantiallythe same time under the foregoing circumstances notwithstanding theirdifferences in porosity. The fact that they melt substantiallysimultaneously is unexpected because they are so different in porosity.

It will be appreciated that the bodies 11 may be made of other resins ofpolyethylene and in other sizes, which includes other diameters, otherlengths, and other wall thicknesses. It will also be appreciated, asnoted above, that the porous high density polyethylene which is used forend members 14 can be made in other stiffnesses, other thicknesses andother porosities also if desired. The changes in parameters of thebodies 11 and end members 14 may require changes in the vibratorywelding parameters.

The granular material 23 which was actually used in the canisters 10 isknown as Crosfield white silica gel having a particle size of about0.5-1 millimeter, and the canisters 10 containing such silica gel areintended for use in adsorbing moisture in various environments such aspharmaceutical containers, food containers, and in any otherenvironments where moisture adsorption is desired. It will beappreciated, however, that any other type of granular or nongranulargas-treating material can be used including by way of example and not oflimitation such materials as activated charcoal, molecular sieve,activated bentonite, montmorillonite, calcium sulfate, Clintolite andcrystalline metal aluminosilicates. The canisters can also contain anyother suitable product including but not limited to conventional oxygenabsorbing compositions and conventional carbon dioxide absorbingcompositions. The foregoing products absorb or adsorb gases from theenvironments in which the canisters are placed. However, the canisterscan also contain products which produce vapors which pass into theenvironment in which the canisters are located, and such vapors, by wayof example and not of limitation, are fragrances and carbon dioxide.Therefore, the material within the canister body 11 will becharacterized as "gas treating."

In addition to the foregoing, while the specific material of canister 10has been described above as being high density polyethylene, it is to beunderstood that polypropylene can also be used for both the body 11 andthe porous member 14, and the parameters for effecting the vibratorywelding will have to be adjusted accordingly. It is also believed thatother resins may also be used to provide canisters of the type depictedin FIGS. 1-4 wherein the porous ends are bonded at multiple annularlocations as described above. These other resins, by way of example andnot of limitation, may include nylon, polyvinylidene fluoride (PVDF),polytetrafluoroethylene (PTFE), styrene-acrylonitrile (SAN), polysulfone(PS), ethylene-vinyl acetate (EVA), polycarbonate (PC), polyphthalatecarbonate (PPC) and polyether sulfone (PES).

While the canister 10 has been described above as having two porous endmembers 14, it will be appreciated that it can be fabricated with onlyone porous end, such as 14, and with another end which is not porous,and the other end may be formed integrally with the body or attachedthereto. Also, while the canister has been described as containing agas-treating composition, it is believed that it has generalapplicability irrespective of its contents. In this respect, forexample, it may contain a product which must be allowed to breathe butwhich does not otherwise absorb, adsorb, or in any other way interactwith gases outside of the canister.

While preferred embodiments of the present invention have beendisclosed, it will be appreciated that it is not limited thereto but maybe otherwise embodied within the scope of the following claims.

What is claimed is:
 1. A method of fabricating a canister comprising thesteps of providing an elongated tubular plastic body having an innersurface and an outer surface and an edge portion on said body definingan opening and an end on said edge portion, positioning a porous plasticmember across said opening and in engagement with said end, applyingpressure to said member to force a first portion of said member againstsaid end and to force a second portion of said member located inwardlyof said first portion into said opening, and applying vibratory weldingenergy to said member to effect a first fusion between said firstportion of said member and said end and to also effect a second fusionbetween said second portion of said member and said inner surface ofsaid edge portion adjacent said end, said second fusion extending in adirection transverse to said first fusion.
 2. A method as set forth inclaim 1 wherein said body has a second edge portion defining a secondopening and a second end on said second edge portion, filling said bodywith material through said second opening, positioning a second porousplastic member across said second opening and in engagement with saidsecond end, applying pressure to said second member to force a firstportion of said second member against said second end and to force asecond portion of said second member located inwardly of said firstportion of said second member into said second opening, and applyingvibratory welding energy to said second member to effect a third fusionbetween said first portion of said second member and said second end andto also effect a fourth fusion between said second portion of saidsecond member and said inner surface of said second edge portionadjacent said second end, said fourth fusion extending in a directiontransverse to said third fusion.
 3. A method as set forth in claim 1wherein said first portion has an outer edge, and trimming said outeredge of said first portion of said member to separate it from theremainder of said member.
 4. A method as set forth in claim 2 whereinsaid first portions of said first and second plastic members have outeredges, and trimming said outer edges of said first portions of saidfirst and second members, respectively, to separate them from theremainder of said first and second members, respectively.
 5. A method offabricating a canister comprising the steps of providing a plurality ofelongated tubular plastic bodies each having inner surfaces and outersurfaces and edge portions on said bodies defining openings and ends onsaid edge portions, positioning a porous plastic member across saidopenings of said plurality of bodies and in engagement with said ends ofsaid bodies, applying pressure to said member to force first portions ofsaid member against said ends and to force second portions locatedinwardly of said first portions into said openings, and applyingvibratory welding energy to said member to effect a first fusion betweensaid first portions of said member and said ends and to also effect asecond fusion between said second portions of said member and said innersurfaces of said edge portions adjacent said ends, said second fusionextending in a direction transverse to said first fusion.
 6. A method asset forth in claim 5 wherein said bodies have second edge portionsdefining second openings and second ends on said second edge portions,filling said bodies with material through said second openings,positioning a second porous plastic member across said second openingsand in engagement with said second ends, applying pressure to saidsecond member to force first portions thereof against said second endsand to force second portions located inwardly of said first portions ofsaid second member into said second openings, and applying vibratorywelding energy to said second member to effect a third fusion betweensaid first portions of said second member and said second ends and toalso effect a fourth fusion between said second portions of said secondmember and said inner surfaces of said second edge portions adjacentsaid second ends, said fourth fusion extending in a direction transverseto said third fusion.
 7. A method as set forth in claim 5 wherein saidfirst portions have outer edges, and trimming said outer edges of saidfirst portions of said member to separate them from the remainder ofsaid member.
 8. A method as set forth in claim 6 wherein said firstportions of said first and second members have outer edges, and trimmingsaid outer edges of said first portions of said first and secondmembers, respectively, to separate them from the remainder of said firstand second members, respectively.
 9. A method of fabricating a canistercomprising the steps of providing an elongated tubular plastic bodyhaving an inner surface and an outer surface and an edge portion on saidbody defining an opening and an end on said edge portion which extendsat an angle to said inner surface, positioning a porous plastic memberacross said opening and in engagement with said end, applying pressureto said member to force a first portion of said member against said endand to force a second portion of said member located inwardly of saidfirst portion into said opening such that said second portion extendsalong said inner surface and extends at substantially the same angle tosaid first portion as said end extends to said inner surface, andapplying vibratory welding energy to said member to effect fusionbetween said first portion of said member and said end and to alsoeffect fusion between said second portion of said member and said innersurface of said edge portion adjacent said end, said member beingsufficiently stiff so as not to buckle when subjected to said vibratorywelding energy.
 10. A method of fabricating a canister as set forth inclaim 9 including an outer edge on said first portion, and trimming saidouter edge of said first portion of said member to separate it from theremainder of said member.
 11. A method of fabricating a canistercomprising the steps of providing an elongated tubular plastic bodyhaving an inner surface and an outer surface and an edge portion on saidbody defining an opening and an end on said edge portion which extendsat an angle to said inner surface, positioning a porous plastic memberacross said opening and in engagement with said end, applying pressureto said member to force a first portion of said member against said endand to force a second portion of said member located inwardly of saidfirst portion into said opening, applying vibratory welding energy tosaid member to effect fusion between said first portion of said memberand said end and to also effect fusion between said second portion ofsaid member and said inner surface of said edge portion adjacent saidend such that said second portion extends at substantially the sameangle to said first portion as said end extends to said inner surface,said body having a second edge portion with a second portion of saidinner surface defining a second opening and a second end on said secondedge portion which extends at an angle to said portion of said innersurface, filling said body with material through said second opening,positioning a second porous plastic member across said second openingand in engagement with said second end, applying pressure to said secondmember to force a first portion of said second member against saidsecond end and to force a second portion of said second member locatedinwardly of said first portion of said second member into said secondopening such that said second portion of said second member extendsalong said second portion of said inner surface at substantially thesame angle to said first portion of said second member as said secondportion of said inner surface extends to said second end, and applyingvibratory welding energy to said second member to effect fusion betweensaid first portion of said second member and said second end and to alsoeffect fusion between said second portion of said second member and saidsecond portion of said inner surface of said second edge portionadjacent said second end, both said member and said second member beingsufficiently stiff so as not to buckle when subjected to said vibratorywelding energy.
 12. A method of fabricating a canister comprising thesteps of providing a plurality of elongated tubular plastic bodies eachhaving an inner surface and an outer surface and an edge portion on saidbody defining an opening and an end on said edge portion which extendsat an angle to said inner surface, positioning a porous plastic sheetacross said openings of said plurality of bodies and in engagement withsaid ends of said bodies, applying pressure to said plastic sheet toforce first portions of said plastic sheet against said ends and toforce second portions of said plastic sheet located inwardly of saidfirst portions into said openings such that said second portions extendalong said inner surfaces and extend substantially at the same angle tosaid first portions as said ends extend to said inner surfaces, andapplying vibratory welding energy to said member to effect fusionbetween said first portions of said plastic sheet and said ends and toalso effect fusion between said second portions of said plastic sheetand said inner surfaces of said edge portions adjacent said ends, saidmember being sufficiently stiff so as not to buckle when subjected tosaid vibratory welding energy.
 13. A method of fabricating a canistercomprising the steps of providing an elongated tubular plastic bodyhaving an edge portion with an inner surface and an outer surface and anend on said edge portion with said edge portion defining an opening,positioning a substantially planar porous plastic member across saidopening and in engagement with said end, applying pressure to saidporous plastic member to compress and force an outer portion of saidporous plastic member against said end and to force a substantiallyentirely uncompressed inner portion of said member into said openingwith said inner portion having an outer surface which is adjacent tosaid inner surface of said plastic body, and applying vibratory weldingenergy to said member to effect fusion between said outer portion ofsaid member and said end and to also effect fusion between said outersurface of said inner portion of said member and said inner surface ofsaid edge portion with said outer surface of said inner portion of saidmember being of substantially the same shape as said inner surface ofsaid outer edge portion of said plastic body before said inner portionof said member was forced into said opening.
 14. A method of fabricatinga canister comprising the steps of providing an elongated tubularplastic body having an edge portion with an outer surface and an innersurface and an end on said edge portion with said edge portion definingan opening, positioning a substantially planar porous plastic memberacross said opening and in engagement with said end, applying pressureto said porous plastic member to compress and force an outer portion ofsaid porous plastic member against said end without substantiallychanging the shape of said end on said edge portion and to force asubstantially entirely uncompressed inner portion of said member intosaid opening without substantially changing the shape of said innersurface of said edge portion and with said inner portion having an outersurface which is adjacent to said inner surface of said edge portion,and applying vibratory welding energy to said member to effect fusionbetween said outer portion of said member and said end and to alsoeffect fusion between said outer surface of said inner portion of saidporous plastic member and said inner surface of said edge portion.
 15. Amethod of fabricating a canister as set forth in claim 14 including thestep of trimming said outer portion of said porous plastic member.
 16. Amethod of fabricating a canister as set forth in claim 14 wherein saidelongated tubular plastic body has a second edge portion defining asecond opening, and inserting gas-treating material into said elongatedtubular plastic body through said second opening.
 17. A method offabricating a canister as set forth in claim 14 wherein said vibratorywelding energy produces a bead of fused plastic at the edge of saidouter surface of said inner portion of said porous plastic member.
 18. Amethod of fabricating a canister as set forth in claim 14 wherein saidelongated tubular plastic body has a second edge portion with a secondouter surface and a second inner surface and a second end on said secondedge portion with said second edge portion defining a second opening,positioning a second substantially planar porous plastic member acrosssaid second opening and in engagement with said second end, applyingpressure to said second porous plastic member to compress and force anouter portion of said second porous plastic member against said secondend without substantially changing the shape of said second end on saidsecond edge portion and to force a substantially entirely uncompressedinner portion of said second porous plastic member into said secondopening without substantially changing the shape of said second innersurface of said second edge portion and with said inner portion of saidsecond porous plastic member having an outer surface which is adjacentsaid second inner surface of said second edge portion, and applyingvibratory welding energy to said second porous plastic member to effectfusion between said outer portion of said second porous plastic memberand said second end and to also effect fusion between said outer surfaceof said inner portion of said second porous plastic member and saidsecond inner surface of said second edge portion.
 19. A method offabricating a canister as set forth in claim 18 including the step ofinserting gas-treating material into said tubular plastic body throughsaid second opening before positioning said second substantially planarporous sheet-like member across said second opening.
 20. A method offabricating a canister as set forth in claim 18 wherein said vibratorywelding energy applied to said second porous plastic member produces abead of fused plastic at the edge of said outer surface of said innerportion of said second porous plastic member.